Fluorescent Visualization of Bond Breaking in Polymer Glasses

Mechanofluorescentpolymer probes were used to visualize stressesand bond scission in polystyrene and polycarbonate. Sonication ofpolystyrene probes with a molar mass of 1.1 x 10(5) g center dot mol(-1) in solution resulted in 30% activation after 1 h,while shorter probes showed lower activation percentages. Single-asperitysliding friction tests were performed on mechanophore-containing polystyrene and polycarbonatefilms. Polystyrene showed clearly visible crack formation with a correlatedpattern in the friction force, penetration depth, and fluorescentactivation of the mechanophore. Significant mechanophore activationin polystyrene was observed for an applied normal load of 100 mN,whereas in polycarbonate, activation only occurred at a normal loadhigher than 400 mN. The different degrees of activation correlatewell with the toughness of polycarbonate compared to polystyrene.